Process for applying metallic coatings to porous bases



Patented Dec. 1, i925. UNITED STATES 1,563,193 PATENT OFFICE- v KURT BIPPER, OF VIENNA, AUSTRIA, ASSIGNOR T0 FRITZ POLLAK, OF VIENNA, AUSTRIA.

YROCESS FOR APPLYING METALLIC COATINGS TO POROUS BASES.

1T0 Drawing.

To all whom it may concern: 7 Be it known that I, KURT RIPPER, a citizen of the Republic of Austria, residing at Vienna, Austria, have invented certain new and useful Improvements in a Process for Applying Metallic Coatings to Porous Bases, of whichthe following is a specification.

This invention relates to a process of ap-v plyin metallic coatings to porous bases.

It as long been desired in the art, to apply firmly adherent metallic coatings free from pores to porous articles by electrodeposition. By this means the respective materials are to be protected from the attacks of liquids, atmospheric influences and ases. The electro-plating of such articles,

owever is met with considerable difliculty,

-because both the alteration of the porous manner with surface during the deposition of the metallic coating, as well as also the irregular adhesion of the metallic coating to the base, and finall the small stability of a metallic coating 0 such thinness, must be taken into account.

In order to render the non-metallic surfaces electrically conductive, it is known that preferably graphite isemployed. For this purpose for example finely ground and washed crude natural gra mm is treated first with sulphuric acid, an thereupon with concentrated soda lye in autoclaves under pressure. Accordin to Schtissel (Musspratt, Enzyklopadisc es Handbuch der Technik, 4th edition, volume 4, page 1569) finely ground gra bite is pre-treated in a similar hydrochloric acid and alkali. However even these known purifying processes do not produce gra hltes for rendering porous materials con uctive which fulfil the requirements of the art of electrodeposition, neither does the use ofsynthetic graphite furnish good results. It was hitherto unknown to what reasons. this uncertain and irre lar action of the graphitecoating meth s enerally used for this purpose'is attribute 1e. Nevertheless it is an established fact that the metal forms firmly adherent deposits at only those portions of the porous surfacewhich have been rendered to all intents and purposes absolutely e ually conductive to the electric current. I the current during the electrolytic process anywhere encounters a resistance which Application filed August 21, 1923. Serial No. 658,594.

this purpose it has been recommended to render the graphite coatingwhich as a rule 1s applied mechanically by hand or by means of a brush.more adherent by the use of adhesives or the like. In practice however this measure is completely useless, since although the adhesive causes the graphite powder to adhere, yet it does not ensure even coating of the graphite to the base. Consequently during the electrolytic treatment hollow spaces areformed in the metallic coating which fall ofi already when slightly pressed by the hand, so that the coating by no means answers its desired purpose.

As a result of very exhaustive experiments it has now been found that the suitability of electrically conductive substances for rendering conductive, porous non-metallic bases is essentially dependent on thesize of the particles of these substances bearing a suitable relation to the size of the hollow spaces (i. e., the-pores) of the porous base. It is assumed that this fact is attributable to the capillary action of the porous bases.

There are, however, sizes of particles which even when using coarsely porous bases no longer give corresponding (satisfying) results. This is the size of particles of more than 3 microns (1 micron is 0.001 millimetre). Thus the inefiectiveness of the hitherto usual graphite-coating methodsis explained since as is well known by mechanica disintegration and washing it is hardly possible to produce particles of a size less than 10 micronsJ 7 The required degree of dispersion for the desired purpose may be produced according to the present invention with the aid of the known mechanical means for the production of colloidal suspensions (beatin mills turbo-mixers, or the like) or by c emical methods such as are used for example, in the production of copper bronze. It is also possible to em loy a combination of mechanical and c emical means. The colloidal suspensions of graphite have a particle size of less than 0.1 micron, the size of the by dispersing chemically produced graphite,

which had been mechanically triturated as this base by gentle rub ing.

far as possible, by means of tannic acid and ammonia till it assumes the colloidal state. Gra hite thus treatedis nowada s brought on t e market under the name of deflocculated Acheson graphite. The coarser particles may be removed therefrom by filtration, for which filterin materials or filtering candles ma be use the pores of which do not excee a. certain size. Colloidal metals may be prepared by the methods known in colloid chemistry, for instance by reducing the respective salt solutions. By very careful o erations one may even succeed to obtain a powder of copper sufficiently fine by reducin a solution of copper-sul phate by means 0 zinc dust.

It is of no importance in what manner the dispersion is produced, the only essential is that the size of the particles is smaller than 3 microns. If dispersions of this character are em 10 ed, the conductive coatings can be applie without any difiiculty to preliminarily treated orous nonconductors in very uniform and firmly adherent layers, .the electro-plating being effected thereupon uniformly and in an excellent manner.

The current conductor need not be applied immediately to the porous bases, inasmuch as a thin layerof lacquer may be applied as a first coating. This is often desirable in order to protect the porous material from being attacked by the electroplating liquor. When operating in this manner the desired effect is produced even when the varnish coating has entirely clogged the pores. This peculiar phenomenon may be explained by the action of the high pressure of precipitation in the electrolytic bath. The layer of varnish is pressed into the porous substance and the small particles of the current conductor arrive in the same way to the surface of the porous base as if they had been ap plied wlthout preliminary varnishing of t e article.

For carrying out the rocess, a wooden object for example is pre iminaril treated with a araflin. or retene mass, t ereupon provide with a thin varnish coating and a colloidal suspension of raphite is applied to A completely uniform and smooth coating of metallic lustre is immediately produced which adheres with extraordinary firmness and can only be removed with difficulty by mechanical means.

On being immersed into the electrolytic bath the iece of wood which has been rendered con uctive is coated with a firmly adherent smooth coatin of the corresponding metal. It isof particu ar importance that the growth closure) of the metallic coating takes place t e more rapidly the smaller the size of the particles of graphite or other disperse con ductive material. p

In the same way also other porous bodies, for example leather, concrete, cardboard,

fabrics, as well as pressed materials of an kind may be coated with a dense, firmly a herent metal.

Coatings roduced by the resent method essentially differ from those itherto made. The latter are only adhering to metals, out are not firmly adhering to porous softer materials. In contradistinction thereto by the present method even one single, perfectly p ane and small surface of a wooden object may be electroplated without any fear of the metallic layer coming off. This astonishing new effect is in first instance due to the fact that the sufiiciently small particles of the conductive substance are by the deposition pressure of the electrolytic bath driven deep into the orous base and that consequently a kind o1 impregnation of the latter takes place.

What I claim is:

1. A process for applying metallic coatings to non-metallic porous objects, which process consists of rendering the surfaces to be coated conductive by means of conductive substances in such a de ree ofdispersion, that the particles thereo are of smaller size than the pores of the base, and thereafter effecting the galvanization.

2. The process for applying metallic coatings to non-metallic porous objects, which process consists of rendering the surfaces to be coated conductive by means of conductive substances in such a degree of dispersion, that the size of their particles does not exceed 3 microns, and thereafter effecting the galvanization.

3. The process for applying metallic coatings to non-metallic porous objects, which process consists of rendering the surfaces to be coated conductive by means of colloidal suspensions of conductive substances, and thereafter effecting the galvanization.

4. The process for applying metallic coatingsto non-metallic porous objects, which process consists of rendering the surfaces to be coated conductive by means of colloidal suspensions of graphite,-and thereafter effectin the galvanization.

5. %he process for applying metallic coatings to non-metallic porous objects, which process consists of rendering the surfaces to be coated conductive by means of colloidal suspensions of graphite, the particles of which have a size of less than 0.1 microns, and thereafter effecting the galvanization;

6. The process for applying metallic coatings to non-metallic porous objects, which consists of first coating the porous base with a layer ada ted to protect the porous me.-

terial from eing attacked by t e galvanic bath, then rendering the surfaces conductive by applying thereto conductive substances in such a degree of dispersion, that the size of their particles does not exceed 3 microns and thereafter effecting the galvanization.

7. The process for applying metallic coat-' ings to non-metallic porous objects, which consists of first coating the porous base with a layer adapted to protect the rous material from being attacked by t e galvanic bath, then rendering the surfaces conductive by applying thereto colloidal suspensions of conductive substances, and thereafter effecting the galvanizat-ion.

8. The process for applying metallic coatings to non-metallic porous objects, which consists of first coating the porous base with a layer adapted to protect the porous material from being attacked by the galvanic bath, then rendering the surfaces conductive by applying thereto colloidal suspensions of graphite, and thereafter eifecting the galvanization.

9. The process for applying metallic coatings to non-metallic porous objects, which consists of first coating the orous base with a layer of a wax-like mass, t en rendering the surfaces conductive by applying thereto conductive substances the size of the particles of which does not exceed 3 microns, and finally effecting the galvanization.

10. The process for applying metallic coat ings to wooden objects, which consists of preliminary treating them with a wax-like mass, nish, then rendering the surfaces conductive by applying thereto conductive substances coating them with a thin layer of var-.

preliminarily treating them with a wax-like mass, coating them with a thin layer of varnish, then rendering the surfaces conductive by applying thereto colloidal suspensions of conductive substances, and finally eflecting the galvanization.

12. The process for applying metallic coatings to wooden objects, which consists of preliminarily treating them with a wax-like mass, coating them with a thin layer of varnish, then rendering the surfaces conductive by applying thereto colloidal suspensions of graphite, and finally effecting the galvanization.

13. The process of applying metallic coatings to a wooden object which consists of preliminarily treating the said base with paraffin, then coating it with a thin layer of varnish, rendering the surfaces to be coated conductive by gently rubbing a colloidal suspension of graphite thereon and finally immersing the piece thus prepared into the galvanic bath.

In testimony whereof I have affixed my signature.

KURT RIPPER. 

